Specifications

Data Parameters Engine Parameters

• 1996–99 6-cylinder 2.5L (323i/is) and 2.8L (Z3) using the MS41.1 controller

These use only one pre or before CAT (upstream) oxygen sensor mounted in the exhaust header

pipe (O2 SENSOR 1) and one post or rear CAT (downstream) oxygen sensor mounted after the

one catalytic converter.

For other OBD-II inline 6-cylinder engines, O2 SENSOR BEFORE CAT1 refers to the upstream

O2S in the front exhaust manifold (cylinders one to three), O2 SENSOR BEFORE CAT2 refers to

the upstream O2S in the rear exhaust manifold (cylinders four to six), and O2 SENSOR AFTER

CAT 1 refers to the downstream O2S for the front exhaust manifold. O2 SENSOR AFTER CAT 2

refers to the downstream O2S for the rear exhaust manifold.

M62TU engine (ME 7.2) uses two warm-up CATs and two main CATs. E46 uses two integral

CATs to front and rear exhaust manifolds.

O2S Location: 8–12 Cylinder Engines

For OBD-II V8 engines, O2 SENSOR 1 (before CAT) and O2 SENSOR AFTER CAT refer to the

cylinder bank including cylinder #1. Cylinder #1 is on the passenger side (right), and O2

SENSOR BEFORE CAT2 and O2 SENSOR AFTER CAT2 refer to driver (left) side bank.

For OBD-I V8 engines, O2 SENSOR 1 refers to bank 1 (cylinder 1 bank) or passenger side of

engine. O2 SENSOR 2 refers to bank 2 or driver's side of engine.

For OBD-II V12 engines with 2 separate engine control systems, each bank runs independently

with separate catalytic converters.

• DME 1—bank 1 (passenger-side), cylinders 1–6

• DME 2—bank 2 (driver-side), cylinders 7–12

The M73TU engine (1999–2001 V12) has an electrically-heated CAT.

For OBD-I V12 engines with two separate engine control systems, each bank runs independently

with separate CATs, but there are no downstream O2Ss, only one OXYGEN SENSOR (pre-CAT)

located on each bank.

The scan tool calls bank 1, the passenger side, “ENGINE (RIGHT)” and bank 2, the driver's side,

“ENGINE (LEFT)”. Long intake runners with each bank's MAF sensor are physically located on

the opposite side of the engine.

Some models are equipped with an exhaust temperature sensor at the catalyst. The sensor is a

PTC resistor which allows the ECM to monitor the catalyst temperature. This input is used for

mixture control and for catalyst efficiency. In the event of an overheat situation, the ECM will

illuminate the Malfunction Indicator Light (MIL) and set a fault code. Under certain load

conditions, the fuel mixture is enriched to aid in cooling down the catalytic converters.

O2 SENSOR HEATER BEFORE CAT

O2 SENSOR HEATER AFTER CAT

Range: __________________________________________________________ ON/OFF

O2 SENSOR HEATER BEFORE CAT(%)

O2 SENSOR HEATER AFTER CAT 1(%)

O2 SENSOR HEATER AFTER CAT 2(%)

Range: _________________________________________________________ 0 to 100%

These parameters indicate the status of the heated oxygen sensor (HO2S) heater circuit. Reads

ON when the ECM is commanding the heater on. On some early systems, the ECM controls the

heat intensity by modulating the duty cycle of the signal to the heater relay. On later models, the

DME typically controls the O2 heater directly. Either system displays a percentage, the higher the

percentage, the greater the heat intensity. At cold start, the downstream O2S duty cycle is